Catalysts 2012, 2, 56-67; doi:10.3390/catal2010056
OPEN ACCESS
catalysts
ISSN 2073-4344
www.mdpi.com/journal/catalysts
Article
Hydrogen Evolution from Napiergrass by the Combination
of Biological Treatment and a Pt-Loaded
TiO2-Photocatalytic Reaction
Tsutomu Shiragami 1, Takayuki Tomo 1, Hikaru Tsumagari 1, Yasuyuki Ishii 2 and
Masahide Yasuda 1,*
1
2
Department of Applied Chemistry, Faculty of Engineering, University of Miyazaki,
Gakuen-Kibanadai Nishi, Miyazaki 889-2192, Japan;
E-Mails: [email protected] (T.S.); [email protected] (T.T.);
[email protected] (H.T.)
Department of Biological Production and Environmental Science, Faculty of Agriculture,
University of Miyazaki, Gakuen-Kibanadai Nishi, Miyazaki 889-219, Japan;
E-Mail: [email protected]
* Author to whom correspondence should be addressed; E-Mail: [email protected];
Tel./Fax: +81-985-58-7314.
Received: 11 November 2011; in revised form: 1 December 2011 / Accepted: 12 December 2011 /
Published: 22 December 2011
Abstract: Ethanol and pentose were produced from lignocellulosic napiergrass by the
simultaneous saccharification and fermentation process (SSF) using hydrolytic enzyme and
S. Cerevisiae. After the ethanol was removed, the pentose solution was subjected to
photocatalytic hydrogen evolution with Pt-loaded TiO2 under UV-irradiation. This process
converted 100 g of napiergrass into 12.3 g of ethanol and 1.76 g of hydrogen whose
total combustion energy of (∆H) was 615 kJ. This was close to the ∆H (639 kJ) of the
pentose (13.6 g) and hexose (27.4 g) obtained by the cellulose-saccharification of 100 g
of napiergrass.
Keywords: TiO2; lignocellulose; hydrolytic enzyme; simultaneous saccharification and
fermentation process; hydrogen-evolution
Catalysts 2012, 2
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1. Introduction
Bio-fuel has been receiving a great amount of interest from the standpoint of utilizing renewable
resources [1]. However, commercially available bio-ethanol has been prepared from the starch of
maize, sugarcane, and sugar sorghum, which are in competition with food sources for human
consumption [2]. Therefore, we are interested in herbaceous lignocellulosic napiergrass (Pennisetum
purpureum Schumach) which is a kind of pasture used in stock farms and therefore, is not in
competition with food sources [3]. Recently we have reported the production of bio-ethanol from
napiergrass through an enzymatic saccharification and a fermentation with yeast (Saccharomyces
cerevisiae) [4]. In this process, 8.8 g of ethanol was produced from 100 g of the leaf part of napiergrass
which contained 44 g of cellulosic components. Thus the ethanol yield was low because of the high
content of hemicellulose composed by pentose which cannot be fermented into ethanol by yeast.
Therefore, the transformation of pentose into bio-fuels is an unavoidable process in the lignocellulosic
biomass conversion. Photocatalytic hydrogen production, using hexose and pentose acting as a
sacrificial reagent, is a prospective candidate to transform pentose into bio-fuels [5–7].
It is well-known that the photocatalytic hydrogen-evolution from H2O by a Pt-loaded TiO2
(Pt/TiO2) is initiated by the charge-separation on TiO2 under photoexcitation [8]. The electron reduced
water to generate H2 on the Pt-loaded on TiO2 (Equation 1). Although the oxidation pathway of
sacrificial saccharides (1) by the hole (h+) is still unclear, Fu et al. have postulated a mechanism by
which the h+ oxidizes directly with the alcohol moiety of glucose [7]. We have proposed that the h+
oxidize the HO− to produce HO radical which oxidize 1 through the hydrogen abstraction from the
α-carbon of the alcoholic and formyl groups [5]. Formally the reaction of 1 with four equivalents of
HO radical, eliminated one mole of CO2 and three moles of H2O (Equation 2). At the same time, it is
expected that 2 equivalents of H2 was evolved by the reduction of water with 4-electrons.
Here, we examined the hydrogen evolution using 1 obtained from napiergrass through the
combination of biological treatment (Equations 3 and 4) and the subsequent photocatalytic reaction
with the Pt/TiO2 catalyst.
TiO2
4 hν
4 e- + 4 h+
4 e- + 4 H2O
2 H2 + 4 HO-
4 h+ + 4 HO-
4 HO
OH O
(1)
OH O
C H + 4 HO
H C
n-1
H
1
(C6H10O5)n
+ n H2O
(C5H8O4)n
+ n H2O
H C
C H + CO2 + 3 H2O
n-2
H
Hydrolytic enzyme
Hydrolytic enzyme
(2)
n C6H12O6
(3)
n C5H10O5
(4)
Catalysts 2012, 2
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2. Results and Discussion
2.1. Alkali-Treatment of Napiergrass
The stem part of a dwarf type of napiergrass was dried and powdered by a blender until the powder
passed through a sieve with 150 μm of mesh. The powdered napiergrass (5.0 g) was treated with a 1%
aqueous solution of NaOH at 95 °C for 1 h in order to remove colored materials such as lignin and
chlorophyll, which disturbed the light-absorption of the photocatalyst. The holocellulose (a mixture of
cellulose and hemi-cellulose) was isolated as a pale yellow precipitate by centrifugation. The colored
materials were dissolved in the aqueous NaOH solution. Lignin was collected as dark brown
precipitate by centrifugation of the supernatant NaOH solution which was neutralized to pH 5.0 by a
dilute HCl solution. As for the results, 2.70 g (54.0%) of holocellulose and 0.61 g (12.2%) of lignin
were obtained from 5.0 g of powdered napiergrass. The residue (1.69 g, 33.8%) contained ash
components and others.
2.2. Biological Treatment of Holocellulose
The holocellulose was turned into the reducing saccharides (1) by three methods shown in Figure 1.
In Method A, the holocellulose (2.5 g) was turned into pentose and hexose by hydrolytic enzyme
(Equations 3 and 4). The SA was performed using a hydrolytic enzyme (250 mg, Acremozyme,
cellulase from acremonium, Kyowa Kasei) [4] in an acetate buffer solution (60 mL, pH 5.0) for 48 h
under vigorous shaking at 45 °C. The solution was subjected to centrifugation to produce the
supernatant solutions (1a) containing both pentose (0.63 g) and hexose (1.27 g). HPLC analysis
showed that the pentose and hexose were mainly xylose and glucose, respectively. Holocellulose was
recovered in 0.49 g, which was 80.4% of the conversion of saccharification.
After the Method A, the 1a was subjected to the fermentation in an acetate buffer solution (180 mL,
pH 5.0) containing the 1a (12.49 g) and the suspension solution (3.6 mL) of S. cerevisiae at 35 °C
(Method B). The reaction was monitored by the CO2-evolution (Equation 5). After the CO2-evolution
was stopped for 107 h, ethanol (3.2 g) was formed. Pentose (3.6 g) was remained without a reaction.
After the ethanol was removed from the reaction mixture by evaporation under reduced pressure, an
aqueous pentose solution (1b) was obtained and subjected to the following photocatalytic reaction.
C6H12O6
S. cerevisiae
2 C2H5OH + 2 CO2
(5)
In Method C, the holocellulose was converted into ethanol and pentose by the simultaneous
saccharification and fermentation process (SSF) according to Equations 3, 4, and 5. SSF was performed
in an acetate buffer solution (180 mL, pH 5.0) containing holocellulose (16.2 g), Acremozyme (3.0 g),
and the suspension solution (3.6 mL) of S. cerevisiae. The CO2-evolution was stopped for 89 h. The
SSF process produced ethanol (3.69 g) and pentose (3.85 g). The ethanol was removed by evaporation
of the solution to produce an aqueous pentose solution (1c). Table 1 summarizes the products yields
based on 100 g of napiergrass.
Catalysts 2012, 2
59
Figure 1. Conversion from napiergrass to the saccharides (1). Operation: (i) the alkali
treatment to remove lignin and others, (ii) saccharification with cellulase (SE) for 48 h, (iii)
fermentation with Saccharomyces cerevisiae (FE) for 107 h, (iv) distillation under reduced
pressure to isolate ethanol, (v) simultaneous saccharification and fermentation (SSF) of
holocellolose using Acremozyme and S. cerevisiae for 89 h.
Napiergrass
i
ii
Hexose + Pentose (1a)
Lignin and
coloured materials
1) iii
2) iv
Method A
Pentose (1b) Method B
Hollocellulose
Ethanol
1) v, 2) iv
Pentose (1c)
Method C
Table 1. The yields of products obtained by the biological and photocatalytic treatments of
the holocellulose occurring in napiergrass a.
Biological treatment
Method b
Product (yields/g) c
A (SA)
Pentose (13.6) →
Hexose (27.4) →
B (SA/FE) Pentose (12.0)
Pentose (12.1) →
Hexose (27.2) → Hexose (0.9) →
EtOH (10.7)
C (SSF)
Pentose (12.8) →
Ethanol (12.3)
a
PC-treatment d
[N] e (yield/g) f
H2 [8.7] (4.23)
∆H/kJ g
603
555
H2 [9.7] (1.66)
H2 [10.2] (1.74)
615
Holocellolose (54.0 g), lignin (12.2 g), and others (33.8 g) was obtained by alkali-treatment of
napiergrass (100 g). b SA = the saccarification with Acremozyme for 48 h, FE = the fermentation
with S. cerevisiae for 107 h, SSF = the simultaneous saccharification and fermentation with
Acremozyme and S. cerevisiae for 89 h. c Product yield based on the 54.0 g of holocellulose
produced 100 g of napiergrass. d The photocatalytic reaction (PC) with Pt/TiO2 of saccharide
solution. In Methods B and C, ethanol was removed before PC reaction. e The limiting hydrogen
mole (N) obtained from the intercept of Figure 2. f The amount of H2 = 2 N (WP/150 + WH/180)
where WP and WH denoted the weight of pentose and hexose. g Total combustion energy
(∆H/kJ mol−1) of H2 and ethanol where ∆H = ethanol (1367) and hydrogen (285). The ∆H of the
mixture of hexose (27.2 g) and pentose (12.0 g) was calculated to be 639 kJ where the ∆H of
glucose was 2803 and ∆H of pentose was calculated to be 2336 kJ mol−1 by 2803 × 5/6. Data were
referred from reference [9].
Catalysts 2012, 2
60
Figure 2. Dependence of H2/1 on 1 used in photocatalytic hydrogen evolution from 1a (●),
1b (◯), and 1c (◇). Reaction conditions: catalyst = 100 mg, water = 150 mL. Intercept
(N) = 8.7 (1a), 9.7 (1b), and 10.2 (1c).
H2/1 (mol/mol)
12
10
8
6
4
2
0
0 .0
0 .5
1 .0
1 .5
2 .0
1 /c a ta ly s t (g /g )
2.3. Photocatalytic Hydrogen Evolution (PC) Using the Saccharide (1) as Sacrificial Agent
The Pt/TiO2 (100 mg) was suspended in an aqueous solution (150 mL) containing 1 (0–249 mg) and
the oxygen was purged by bubbling with N2. The suspended solution was irradiated by a high-pressure
mercury lamp under vigorous stirring with a magnetic stirrer. The band gap of anatase-type of TiO2 is
known to be 3.20 eV which is corresponding to 385 nm. Therefore, the TiO2 can be excited by
366 nm-emission from high-pressure mercury lamp [10]. The evolved gas was collected by
mess-cylinder to measure the total volume of the evolved gas. The irradiation was performed until the
gas evolution ceased. The quantitative analysis of hydrogen, oxygen, nitrogen, and carbon dioxide
were performed by GLC. The results are shown in Table 2. Figure 3 shows the plots of the evolved H2,
CO2, and O2 volumes against the amounts of 1 used. The evolved H2 and CO2 volumes increased
gradually with the increase of 1. When smaller amounts of 1 were used, the volume ratio of H2 to CO2
(H2/CO2) exceeded over 2.0 which was the stoichiometric value of Equations 6 and 7, because of the
dissolution of CO2 into aqueous reaction solution (Table 2). However, with the use of higher amounts
of 1, the H2/CO2 became close to 2.0.
Moreover, it was confirmed that the H2 evolution from water was small (2 mL) in the absence of the
sacrificial reagent. At the same time, 18 mL of O2 was evolved. Therefore, the volume ratio of H2
became O2 (H2/O2) in the photocatalytic reaction over stoichiometric value (2.0) [11]. Also, in the
presence of sacrificial agent, a considerable amount of O2 was evolved. At the present time, the
evolution mechanism of O2 is still under investigation. Other gases such as CH4 and CO [12] were not
observed in the evolved gas.
Catalysts 2012, 2
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Figure 3. Plots of the volumes of H2 (●), CO2 (○), and O2 (▲) against the amounts of 1
used in the photoreaction of 1a (A), 1b (B), and 1c (C) with the Pt/TiO2. Reaction
conditions: catalyst = 100 mg, water = 150 mL.
150
120
90
60
30
0
(C)
Evolved gas volume/mＬ
(B)
Evolved gas volume/mＬ
Evolved gas volume/mＬ
(A)
150
120
90
60
30
150
120
90
60
30
0
0
50
100
150
200
250
0
0
1a/mｇ
50
100
150
200
0
1b/mｇ
50
100
150
200
1c/mg
Table 2. Photocatalytic H2 evolution (PC) using the saccharides (1a–1c) as sacrificial agent a.
1/mg b
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1c
1c
1c
1c
1c
1c
a
0
42
83
125
166
208
249
38
75
113
150
188
38
75
113
150
188
225
T/h c
5
10
21
30
49
53
74
17
25
31
45
53
14
26
29
40
53
43
Total
13
72
110
158
184
215
240
80
117
157
160
161
78
134
174
225
225
230
d
Gas volume/mL
H2
CO2
2
0
47
11
75
27
94
35
107
51
120
53
131
70
48
17
81
31
102
36
108
45
104
43
54
15
89
33
116
42
142
63
145
67
153
69
O2
18
21
20
29
33
44
40
19
19
26
27
31
21
22
26
20
28
34
e
N2
−7
−7
−12
0
−7
−2
−1
−23
−13
−7
−20
−17
−12
−10
−10
0
−15
−26
Molar ratio
H2/1
H2/CO2
8.4
4.3
6.7
2.8
5.6
2.7
4.8
2.1
4.3
2.3
3.9
1.9
8.6
2.9
7.2
2.6
6.1
2.8
4.8
2.4
3.7
2.4
9.6
3.6
8.0
2.7
6.9
2.8
6.3
2.3
5.2
2.2
4.6
2.2
Irradiation was performed for an aqueous solution (150 mL) containing 1 and Pt/TiO2 (the Pt
content was 2 wt%, 100 mg); b The saccharides (1a, 1b, and 1c) were obtained from Methods A, B,
and C, respectively; c Irradiation time (T) to reach the maximum volume of hydrogen; d The total
gas volume collected over water by mess-cylinder; e The amounts of N2 was calculated by the
subtraction of dead space volume from the measured amounts of N2.
Catalysts 2012, 2
62
According to Equations 6 and 7, the 10 and 12 equivalents of H2 were theoretically obtained from
1 mole of pentose and hexose, respectively. However, the molar ratio of the evolved H2 to 1 (H2/1) did
not reach the theoretical values. Moreover, the H2/1 depended on the amount of 1 used. Therefore, the
H2/1 values were plotted against the weight ratio of 1 to catalyst (1/catalyst), as shown in Figure 2. As
the 1/catalyst values decreased, the H2/1 values increased. The intercept of the plots represents the
limiting H2/1 values (N) at an infinite amount of a catalyst. The N values were nearly equaled to the
theoretical values. Judging from these results, it is suggested that the deactivation of the catalyst
occurred at the high turnover.
C5H10O5 + 5 H2O
C6H12O6 + 6 H2O
hν
Pt/TiO2
hν
Pt/TiO2
5 CO2 + 10 H2
(6)
6 CO2 + 12 H2
(7)
The amounts of the hydrogen obtained from the photocatalytic reaction of 1 were estimated by
multiplying N by the moles of 1: The amount of H2 in g = 2 N (WP/150 + WH/180) where WP and WH
denoted the weight of pentose and hexose. The results are shown in Table 1. Thus, the amounts of H2
were determined to be 4.23, 1.66, and 1.74 g from 1a, 1b, and 1c which were derived from 100 g of
napiergrass, respectively.
2.4. The Combustion Energy of the Products
The three processes were compared from the standpoint of the combustion energy (∆H/kJ mol−1) of
the bio-fuel produced by biological treatment and PC reaction, as shown in Table 1. The Method A
process and PC produced 4.23 g of H2. The total ∆H was calculated to be 603 kJ using the ∆H of H2
(285 kJ mol−1) and ethanol (1,367 kJ mol−1) [9]. The Method B and PC processes produced ethanol
(10.7 g) and H2 (1.66 g) whose total ∆H was 555 kJ. Also the Method C and PC process gave ethanol
(12.3 g) and H2 (1.74 g) whose total ∆H was 615 kJ. Thus, the combination of the SSF process
(Method C) with the PC process was most effective process. This ∆H was close to the 639 kJ which
was ∆H of 27.4 g of hexose and 13.6 g of pentose which were formed from 100 g of napiergrass.
3. Experimental Section
3.1. Preparation of the Photocatalyst
Anatase-type of TiO2 (ST-01) was purchased from Ishihara Sangyo, Japan. According to the
literature [13], an aqueous solution (50 mL) containing TiO2 (1.0 g), K2PtCl6 (10–100 mg), and
2-propanol (0.38 mL) was irradiated by high-pressure mercury lamp for 24 h with stirring to give the
Pt-loaded TiO2 catalyst (Pt/TiO2). The optimized Pt-content on TiO2 was determined to be 2.0 wt% by
the comparison of the amounts of hydrogen-evolution by the Pt-doped TiO2 (100 mg) under irradiation
by high-pressure mercury lamp for 6 h using glucose (100 mg) as sacrificial reagent. Thus the Pt/TiO2
(2 wt% of Pt) was used throughout the present investigation.
Catalysts 2012, 2
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3.2. Analysis
The amount of the saccharides (1) formed by the enzymatic saccharification (SA) process was
analyzed by the modified Somogyi-Nelson method assuming the composition of 1 as C6H12O6 [14].
Also the amounts of hexose and pentose were analyzed by a Shimadzu LC-20AD high-performance
liquid chromatography system using anion exchange column (Shodex Asahipak NH2P-50 4E). Ethanol
concentrations were determined by a Shimadzu GC-2014 gas chromatograph using a glass column of
5% Thermon 1000 on Sunpak-A (Shimadzu) with 2-propanol as an internal standard. Hydrogen,
carbon dioxide, and nitrogen were analyzed on a Shimadzu GC-8A equipped with TCD detector at
temperature raised from 40 to 180 °C using a stainless column (3 mmΦ, 6 m) packed with a
SHINCARBON ST (Shimadzu).
3.3. Alkali-Treatment of Napiergrass
A dwarf type of napiergrass (Pennisetum purpureum Schumach; dwarf variety of late-heading
type) [3] was cultivated in the Sumiyoshi Ranch, Faculty of Agriculture, University of Miyazaki. The
powdered stem part of the napiergrass (30 g) was treated with a 1% aqueous solution of NaOH
(400 mL) at 95 °C for 1 h. Holocellulose was isolated as pale yellow precipitate by centrifugation. The
neutralization of the supernatant solution to pH 5.0 by a dilute HCl solution gave a dark brown
precipitate of lignin which was collected by centrifugation.
3.4. Saccharification of Hollocellulose with Enzyme (SA)
The holocellulose (2.5 g) was dispersed in an acetate buffer solution (60 mL, pH 5.0) and a
hydrolytic enzyme (Acremozyme, Kyowa Kasei, 250 mg) was added to the sterile solution. The
saccharification was performed by under vigorous shaking at 45 °C for 48 h [4]. The solution was
subjected to centrifugation at 12,000 rpm to produce the supernatant solutions of 1 which were used in
the following process.
3.5. Fermentation of the Saccharide (1) with S. cerevisiae
Saccharomyces cerevisiae NBRC 2044 was cultured at 30 °C for 24 h in a basal medium (initial
pH 5.5) consisting of glucose (20 g L–1), bactotryptone (1.0 g L–1, Difco), yeast extract (1 g L–1),
NaHPO4 (1 g L–1), and MaSO4 (3 g L–1) [4]. After incubating for 24 h, the cell suspension solution of
S. cerevisiae was obtained. The suspension solution (3.6 mL) of S. cerevisiae was added to a solution
of 1 (180 mL). The fermentation (FE) was performed at 35 °C with stirring using a magnetic stirrer
until the evolution of CO2 was stopped.
The simultaneous saccharification and fermentation process (SSF) was performed as follows. The
holocellulose (16.2 g) was dispersed in an acetate buffer solution (180 mL, pH 5.0) and was sterilized
in autoclave at 120 °C. Acremozyme (3.0 g) and the cell suspension (3.6 mL) of S. cerevisiae were
added to the suspension. The suspension was stirred vigorously with a magnetic stirrer at 35 °C until
the evolution of CO2 was stopped.
Catalysts 2012, 2
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3.6. Photocatalytic Reaction
The catalyst (usually 100 mg) and the aqueous solution of 1 (usually 5.0 mL) were introduced to
a reaction vessel. The volume of the reaction solution was adjusted to 150 mL with water (usually
145 mL). A high-pressure mercury lamp (100 W, UVL-100HA, Riko, Japan) was inserted into the
reaction vessel, which was attached to a mess-cylinder to correct the evolved gas and set in a water
bath to keep it at a constant temperature (usually 20 °C) (Figure 4). After the oxygen was purged by
nitrogen gas, irradiation was performed with vigorous stirring using magnetic stirrer. The evolved gas
was collected by a mess-cylinder to measure the total volume of the evolved gas (Figure 4(A)). The
quantitative analysis of hydrogen, nitrogen, and carbon dioxide were performed by GLC using the
peak area (A) measured by the GLC-analysis, the sample gas volume (V3, 500 μL), and the slopes of
the calibration curves (f) which were determined to be 3380, 334, 388 and 377 for H2, N2, O2, and CO2,
respectively (Figure 4(B)). According to Equation (8) where V1 was the total volume of evolved gas
(mL) corrected by mess-cylinder, V2 was the volume (mL) of the dead space of the vessel before
reaction (usually 230 mL), the amounts of for H2, N2, O2, and CO2 were obtained
The amounts of gas (mL) = A (V1 + V2)/(f × V3)
(8)
In order to efficiently irradiate the Pt/TiO2 suspended in solution, the amount of the Pt/TiO2 was
optimized using 150 mg of 1a. When 100 mg (1.25 mmol) of the Pt/TiO2 (2.0 wt% of Pt content) was
used for an aqueous solution (150 mL), the largest amounts of H2 evolved, as shown in Figure 5.
V1
1.90 N 2
V2
Lamp
1.77 H2
Figure 4. (A) Outlines of photoreaction apparatus and (B) GLC chart of the evolved gas
from the photocatalytic reaction of Pt/TiO2.
Float
Magnetic
stirrer
0.0
2.0
9.49 CO2
1.77 O2
Reaction
vessel
4.0
6.0
8.0
10.0
Retention time (min)
(A)
(B)
Catalysts 2012, 2
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Figure 5. Dependence of H2 volume on the weight of Pt/TiO2 in the photocatalytic
hydrogen evolution using 1a. The irradiation was performed until the H2-evolution stopped.
Reaction conditions: 1a = 150 mg, water = 150 mL.
180
H2/mＬ
160
140
120
100
80
60
40
20
0
0
25
50
75
100 125 150
catalyst/mg
4. Conclusions
The photocatalytic hydrogen production with Pt/TiO2 has been widely developed using methanol [15],
ethanol [16], glycerol [17], pentose [4], glucose [7], carboxylic acids such as glycolic acid [18] and
acetic acid [19]. Recently we have compared the N values among the variety of saccharides and the
related compounds to evaluate their sacrificial ability [4]. We have found the N values of alcoholic
substances such as glycerol and arabitol were nearly equaled to the theoretical amounts (0.5m + 2n − k)
for CnHmOk (Equation 9). On the other hand, the N values of glucose, xylose and the carboxylic
compounds did not reach the theoretical amounts, showing that the sacrificial ability of saccharides
was inferior to those of the alcohols. However, the photocatalytic hydrogen production from pentose is
an important step in the transformation from lignocellulose to bio-fuel. Moreover, there are no reports
on the photocatalytic H2 evolution combined with the biological saccharification of biomass, so far.
CnHmOk + (2n-k) H2O
n CO2 + (0.5m + 2n - k) H2
(9)
The present study showed that saccharides derived from napiergrass could operate effectively as
sacrificial agent with the same activity as pentose [5] and glucose [7]. The SSF process poses an
advantage in the pentose-production from the standpoints of simplicity of the manufacturing process,
shortening of the reaction time, and yield of ethanol. The formed bio-fuel, ethanol and hydrogen, has
almost the same combustion energy (∆H) as saccharide occurring in lignocellulosic napiergrass. If the
UV light in sunlight is used as the light source for catalytic reaction, it will provide a useful method to
produce H2 from pentose.
Catalysts 2012, 2
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References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Ward, O.P.; Singh, A. Bioethanol technology: Development and perspectives. Adv. Appl.
Microbiol. 2002, 51, 53–80.
Balat, M.; Balat, H. Recent trends in global production and utilization of bio-ethanol fuel.
Appl. Energy 2009, 86, 2273–2282.
Ishii, Y.; Mukhtar, M.; Idota, S.; Fukuyama, K. Rotational grazing system for beef cows on dwarf
napiergrass pasture oversown with Italian ryegrass for 2 years after establishment. Grassl. Sci.
2005, 51, 209–220.
Yasuda, M.; Miura, A.; Yuki, R.; Nakamura, Y.; Shiragami, T.; Ishii, Y.; Yokoi, H. The effect of
TiO2-photocatalytic pretreatment on the biological production of ethanol from lignocelluloses.
J. Photochem. Photobiol. A 2011, 220, 195–199.
Shiragami, T.; Tomo, T.; Tsumagari, H.; Yuki, R.; Yamashita, T.; Yasuda, M. Pentose acting as a
sacrificial multi-electron source in photocatalytic hydrogen evolution from water by Pt-doped
TiO2. Chem. Lett. 2012, in press.
Kawai, T.; Sakata, T. Conversion of carbohydrate into hydrogen fuel by a photocatalytic process.
Nature 1980, 286, 474–476.
Fu, X.; Long, J.; Wang, X.; Leung, Y.; Ding, Z.; Wu, L.; Zhang, Z.; Li, Z.; Fu, X. Photocatalytic
reforming of biomass: A systematic study of hydrogen evolution from glucose solution. Int. J.
Hydrog. Energy 2008, 33, 6484–6491.
Fujishima, A.; Rao, T.N.; Tryk, D.A. Titanium dioxide photocatalysis. J. Photochem. Photobiol. C
2000, 1, 1–21.
Gslinska, A.; Walendziewski, J. Photocatalytic water-splitting over Pt-TiO2 in the presence of
sacrificial Reagents. J. Energy Fuels 2005, 19, 1143–1147.
Kitano, M.; Tsujimaru, K.; Anpo, M. Development of water in the separate evolution of hydrogen
and oxygen using visible-responsive TiO2 thin film photocatalysts: Effect of the work function of
the substrates on the yield of the reaction. Appl. Catal. A 2006, 314, 179–183.
Bahruji, H.; Bowker, M.; Davies, P.R.; Pedrono, F. New insights into the mechanism of
photocatalytic reforming on Pd/TiO2. Appl. Catal. B 2011, 107, 205–209.
Atkins, P.W. Physical Chemistry, 5th ed.; Oxford University Press: Oxford, UK, 1994; pp. 922–926.
Kennedy, J.C., III; Datye, A.K. Photochemical heterogeneous oxidation of ethanol over Pt/TiO2.
J. Catal. 1998, 179, 375–389.
Kim, Y.-K.; Sakano, Y. Analyses of reducing sugars on a thin-layer chromatographic plate with
modified Somogyi and Nelson reagents, and with copper bicinchoninate. Biosci. Biotechnol.
Biochem. 1996, 60, 594–597.
Chiarello, G.L.; Aguirre, M.H.; Selli, E. Hydrogen production by photocatalytic stream reforming
of methanol on noble metal-modified TiO2. J. Catal. 2010, 273, 182–190.
Yang, Y.Z.; Chang, C.-H.; Idriss, H. Photo-catalytic production of hydrogen from ethanol over
M/TiO2 catalysts (M = Pd, Pt, or Rh). Appl. Catal. 2006, 67, 217–222.
Daskalaki, V.D.; Kondarides, D.I. Efficient production of hydrogen by photo-induced reforming
of glycerol at ambient conditions. Catal. Today 2009, 144, 75–80.
Catalysts 2012, 2
67
18. Ho, C.-H.; Shieh, C.-Y.; Tseng, C.-L.; Chen, Y.-K.; Lin, J.-L. Decomposition pathways of
glycolic acid on titanium dioxide. J. Catal. 2009, 261, 150–157.
19. Zheng X.-J.; Wei, L.-F.; Zhang, Z.-H.; Jiang, Q.-J.; Wei, Y.-J.; Xie, B.; Wei, M.-B. Research on
photocatalytic H2 production from acetic acid solution by Pt/TiO2 nanoparticles under UV
irradiation. Int. J. Hydrog. Energy 2009, 24, 9033–9041.
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